Pharmacognosy of St. John’s Wort

Introduction:

St. John’s Wort is a commonly found herbal medication which is useful for the treatment of depression and as an antiviral agent. The name St. John’s wort is so called because it’s flowers blossoms around St. John’s day which is celebrated on the 24th of June. It is also known as klamath weed, amber touch-and-heal, rosin rose, goatweed and millepertuis. The major chemical constituent of St. John’s Wort is hypericin which is a phenolic glycoside. St. John’s wort is also included in the British Pharmacopoeia (B.P) and in the United States Pharmacopoeias (USP) as treatment for depression.

St. John’s Wort (Anthraquinones)

Biological Source Dried aerial parts of Hypericum perforatum
Family Hypericaceae (Clusiaceae)
Geographical Source Perennial plant native to Europe. Through colonization it is now also found in USA and parts of Canada and Australia and was initially thought to be a weed.
Morphology/Macroscopical Characters
  • The drug is present in the green oval-shaped leaf fragments, stems, buds and yellow flowers.
  • The name “perforatum” is given to the plant due to the presence of transparent areas on the leaves and petals. These transparent areas comprise of the oil glands. The oil glands may also be present as small dots on the lower surface of the leaves.
  • The leaves are oppositely arranged, sessile, glabrous and 1.5-4 cm in length. The leaves have an elliptical to ovate outline with an entire margin.
  • The stem is hollow and cylindrical with two faint ribs on either side.
  • St.john’s wort has a distinct odour and a sweet and astringent taste.
Microscopic Characters
  • The lower epidermis consists of anomocytic and paracytic stomata.
  • The oil glands are located in the mesophyll and are generally filled with red-colored hypericin. These glands are also found in the petals and sepals.
  • The plant has ellipsoidal pollen grains.
  • The plant lacks trichomes and calcium oxalate crystals which may be present due to adulterants.
Chemistry St. John’s Wart consists of a variety of constituents including napthodianthrones (less than 0.1%-0.15%), flavonoids, phloroglucinols and essential oils.

Structure of hypericin and pseudohypericin - two major constituents of St. John's Wort

Structure of hypericin and pseudohypericin - two major constituents of St. John's Wort

Napthodianthrones-Hypericin(reddish pigment found in concentration of 0.02% -2.5%) and Pseudohypericin are the anthroquinones present. Also present are emodin-anthranol, cyclo-pseudohypericin, isohypericin and protohypericin.
Flavanoids (around 7% in leaves and less than 12% in flowers respectively) include kaempferol, quercitin, isoquercitin, amentoflavone, luteolin, myricetin, hyperin, hyperoside and rutin. Proanthocyanidins (approximately 12% of aerial parts) compose of catechin and epicatechin.
Phloroglucinols-Hyperforin(2%-4% ) adhyperforin and furohyperforin (oxygenated analog) are present.The phloroglucinols represent the major portion of the lipophilic extract of the plant.

Essential oils are present in concentrations of 0.05%-0.9%. It consists of mono- and sesquiterpenes.

Chemical Tests Anthraquinones are generally orange-red compounds which can be extracted and their UV absorbance wavelengths can be checked. Hypericin has a unique UV-visible absorption spectrum and absorbs light with a λmax of 598nm.
Adulterants/Allied drugs/ Substitutes St. John’s wort is a dietary supplement in the USA and is therefore not regulated by the FDA. The hypericin constituent in the formulations can vary between 47% to 165% of labeled hypericin concentrations. Other constituents also vary to great extent depending upon harvest time of the medicine. Thus one should be advised even though the medication may not contain adulterants, activity may change from one formulation to another.
Uses St.John’s wort has potential  antidepressant and antiviral effects. It is also useful as an antibacterial, anti-inflammatory and is known to have wound-healing and skin-healing properties
Other Notes (life cycle, extraction, pharmacology etc.) Proposed Mechanism of Action:

  • Antidepression Activity: Initially it was believed that anti-depressant activity of hypericin was due to inhibition of MAO (monoamine oxidase) enzyme. However, this theory was disproved later. The current belief is that hypericin and other constituents of St. John’s wort inhibit the reuptake of excitatory neurotransmitters such as serotonin, norepinephrine and dopamine.
  • Antiviral and antibacterial Activity: Hypericin and pseudohypericin show antiviral and antibacterial activity due to non-specific association to cellular and viral membranes. It is believed that photoactivation of hypericin (which is known to posses unique spectroscopic properties) results in photo-oxidation of viruses and bacterial cells thus killing them.
  • Wound-Healing Properties: Tannins from the plant show astringent activity that contribute to the wound-healing property.

References:

  1. Trease and Evans’ Pharmacognosy, 16e (Evans, Trease and Evans Pharmacognosy)
    Elsevier: New York, 2009.
  2. Ara DerMarderosian, et. al. The Review of Natural Products 4th Edition.
  3. Kokate, C. K.; Gokhale, S. B.; Purohit, A. P. A textbook of Pharmacognosy, 29th ed.; Nirali Prakashan: Pune, 2009.

About Sweety Mehta

Studied B. Pharm. at Mumbai Educational Trust Institute of Pharmacy (Mumbai). Worked at Cipla, Mumbai as Marketing executive for 2 years and 9 months. Earned a diploma in marketing from Welingkar's Institute of Management Development and Research.